In a waveguide slot array antenna device in which a plurality of slots are formed at a wall surface of a waveguide with a rectangular sectional shape, a waveguide slot array antenna device in which a slot length is approximately ½ the wavelength, and which the slots are arranged at an interval of approximately ½ the guide wavelength (wavelength in waveguide) in a guide axis direction of the waveguide is publicly known.
FIG. 42 is a top view showing a waveguide slot array antenna device of Conventional Example 1.
In FIG. 42, a waveguide 1 has a short-circuit surface 2 at an end section and power is fed from the other side.
A guide axis direction of the waveguide 1 is defined as an x-direction, a direction orthogonal to a guide axis of the waveguide 1 on a wall surface at which a slot 100 is formed is defined as a y-direction, and a normal direction of the wall surface at which the slot 100 is formed is defined as a z-direction.
A waveguide inner wall 3 and a waveguide outer wall 4 respectively show the internal surface of a broad wall surface of the waveguide 1 and the external surface of the broad wall surface of the waveguide 1.
For convenience's sake, a dimension between the waveguide inner walls in the y-direction is denoted as b, and a dimension between the waveguide outer walls is denoted as B.
A narrow wall surface 5 is a wall surface at which the slot 100 is formed.
Respective slots 101 and 102 provided to the narrow wall surface 5 of the waveguide 1 are each inclined by an angle of +τ or −τ with respect to the y-direction orthogonal to the guide axis of the waveguide 1. Adjacent slots are each disposed to be symmetrical with respect to a center line 6 in a waveguide width direction between the adjacent slots.
On this occasion, a dimension of the slot 100 in the y-direction is smaller than the dimension b between the waveguide inner walls.
Impedance is matched by setting the whole length of the slot to be approximately ½ the wavelength to cause resonance for pure resistance and arranging the slot 100 with an inclination by the angle τ as the angle of arrangement for the slot 100 with respect to the y-direction orthogonal to the guide axis of the waveguide 1 to adjust the resistance of the slot 100.
In addition, since an electric field is generated in a width direction of the slot 100, linear polarization with polarization in the guide axis direction as the main polarization is radiated by disposing the respective adjacent slots to be symmetrical with respect to the center line 6 (see Non-Patent Document 1 below).
In the case where the frequency is constant and the dimension B between waveguide outer walls and the dimension b between waveguide inner walls in the y-direction of the waveguide 1 are reduced in the waveguide slot array antenna device of Conventional Example 1, the length of the slot 100 necessary to obtain resonance characteristics is unchanged at approximately ½ the wavelength, and only the dimension B between waveguide outer walls and the dimension b between waveguide inner walls in the y-direction of the waveguide 1 are reduced.
Therefore, in FIG. 42, the dimension of the slot 100 in the y-direction becomes larger than the dimension B between waveguide outer walls in the y-direction of the waveguide 1, the slot 100 protrudes beyond the edge of the waveguide inner wall 3, and a slot length necessary to obtain the resonance characteristics cannot be ensured.
Meanwhile, a method is proposed to ensure the resonance length of a slot such that the slot does not exceed the dimension b between waveguide inner walls by using a crank-shaped slot that is bent in the guide axis direction at both end sections of the slot when the waveguide width is smaller with respect to the slot length.
FIG. 43 is a top view showing a waveguide slot array antenna device of Conventional Example 2.
In FIG. 43, a crank-shaped slot 200 is formed on a wall surface of a coaxial line 201. Those similar to the above are denoted by the same reference numerals, and descriptions thereof will be omitted.
On this occasion, the configuration is such that a dimension of the crank-shaped slot 200 in the y-direction does not exceed a dimension b between waveguide inner walls (see Patent Document 1 below).
Although it is mentioned that the crank-shaped slot 200 is a configuration at the wall surface of the coaxial line 201 described above for resonating the slot 200 in a slot array antenna formed with the crank-shaped slot 200, a method of impedance adjustment for the slot 200 is neither disclosed nor implied.
Particularly, when the crank-shaped slot 200 is used in a waveguide slot array antenna, states of a current flowing in the wall surface of the coaxial line 201 and the waveguide wall surface are different, and an operation of the slots 200 is different accordingly.
Particularly in the case where the crank-shaped slot 200 is applied to a waveguide slot array antenna provided with the slot 100 at the narrow wall surface 5 of the waveguide 1 as shown in FIG. 42, a bent end section of the slot 200 is lengthened in the case where the slot length desired to obtain resonance with respect to the waveguide width is sufficiently long.
Due to this, the bent end section largely blocks a current flowing in the direction y orthogonal to the guide axis of the waveguide 1, thus increasing conductance per single slot.
Thus, in the case where it is necessary to increase the number of slots provided per waveguide, impedance cannot be matched with a waveguide bonding section.
In addition, assuming that the polarization in the guide axis direction is the main polarization, the cross polarization component of a radiation pattern of a single slot increases due to an increase in the electric field component orthogonal to the main polarization generated from the bent end section.